Turner masterpiece mostly displayed in Greek city (6)
I believe the answer is:
thebes
'greek city' is the definition.
(Thebes is a Greek city)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for thebes that I've seen before include "Ancient city of upper Egypt" , "Seven Against - (Aeschylus)" , "Old Egyptian city" , "Old city of Greece or Egypt" , "Classical city" .)